A compact disc (CD) is a disc which is recorded in a format with only a digital audio signal contained in a predetermined frequency band. A video disc is a disc which is recorded in a format with an analog audio signal contained in a frequency band different from the frequency band for the CD mentioned above. Further, the video disc family includes a so-called Laser Vision Disc with Digital sound (LDD) which is recorded in a format with the digital audio signal and the analog audio signal contained in the aforementioned predetermined frequency band and the frequency band different from the predetermined frequency band, respectively.
FIG. 4 shows the frequency spectrum of an RF signal obtained from such an LDD disc. In FIG. 4, A represents the spectrum of stereo audio signals of the left and right channels or two-channel audio signals whose components are digitized, B shows the spectrum of audio FM signals of the two channels, and C shows the spectrum of a video FM signal.
Respective discs of different types, particularly KARAOKE (sing-along type discs), employs a predetermined two-channel monaural recording method in which one of the two-channel audio signals (left and right channel) is a monaural accompaniment and the other is a monaural accompaniment plus vocal. In the aforementioned LDD disc, normally, the analog signal is recorded in such a manner, while the digital audio signal is recorded as a stereo audio signal associated with the content of the analog audio signal. As a further class of discs, the digitized audio signals of some discs are recorded in the predetermined two-channel monaural recording method.
In order to facilitate identification, discs which are recorded in the predetermined two-channel monaural recording method are provided with an identification code indicative of the method (i.e., recording format). Thus, a disc player capable of playing back the discs of different types including KARAOKE discs, can read such identification code (e.g., to identify an LDD disc) to automatically set the reproduction mode to reproduce the audio signals recorded in the aforementioned predetermined two-channel monaural recording method.
The disc player further can be provided with a mixing means for mixing the reproduced signal of the left and right channels for KARAOKE use, so that the sound level of the vocal can be adjusted by means of this mixing means.
When playing back a CD which is not provided with the identification code, or when the LDD disc is to be played back in the stereo mode, it is necessary to select the reproduction mode manually. However, since a disc player typically performs an initialization process with each changing of a loaded disc, to automatically select a reproduction mode in accordance with the discs identification code (i.e., which typically is different from a manually set stereo reproduction mode), the reproduction mode must be manually changed each time the discs are replaced if one prefers to listen to a stereo reproduction.